Ballast apparatus



March 17, 1959 C. E. STRECKER BALLAST APPARATUS Filed April 2, 1956 \J S (0 m) 5(0PEN) \c CB INVENTOR.

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ms ATTORNEY United States Patent O BALLAST APPARATUS Charles E. Strecker, Danville, 11]., assignor to General Electric Company, a corporation of New York Application April 2, 1956, Serial No. 575,451 Claims. (Cl. 315-100) My invention relates to reactor apparatus and, more particularly, to reactor apparatus and circuits generally called ballasts for igniting and operating gaseous discharge devices, such as fiuorescent lamps.

One popular type of ballast apparatus is used in circuits for sequentially igniting and controlling the current to a pair of fluorescent lamps connected in series circuit relation with one another. Such ballasts and circuits are described, for example, in United States Patent 2,358,810-Karash and in United States Patent 2,558,293-Feinberg. In such apparatus, an auxiliary high [reactance element providesvoltage for igniting one of the lamps and the resultant current through this ignited lamp functions in conjunction with other reactance elements in the circuit to ignite the other serially connected lamp and then to ballast both lamps. For economy and simplicity, all of the desired inductive reactance elements are now generally provided by separate secondary windings on a unitary magnetic core structure forming a single high-reactance transformer in which the starting reactance or winding is arranged on one side of the primary winding and the ballasting reactance or winding is on the other side of the primary winding sometimes with a portion thereof wound over the primary winding.

This transformer construction, however, has not heretofore been found suitable in applications where a very close equality or balance in current between the two i lamps is required. This is because the starting winding is connected across only one lamp and the capacitor. The small circulating current drawn by this starting winding during operation of both series-connected lamps produces this unbalance. Difficulties are also encountered in utilizing this construction in applications where an unusually shallow ballast is desired since the requisite longitudinal extension of the ballasting winding to provide the desired open-circuit voltage often increase the reactance of this winding beyond the value which can conveniently be reduced to optimum values by the increased series air gap. of other reactance-reducing means which do not necessitate an increase in height. Another limitation in this conventional transformer construction lies in the relatively high temperature rise in the primary winding under the abnormal condition when the second lamp does not fire or is omitted thereby requiring sufiicient copper in the primary winding to reduce this rise to tolerable values.

Accordingly, an important object of the invention is to 'provide apparatus for sequentially igniting and ballasting a pair of serially connected discharge devices with substantially equal operating currents in both devices. Another object is to provide ballast apparatus for sequentially igniting a pair of serially connecting discharge devices which not only improves the balance in current between the two devices but also reduces lamp current crest factor and third harmonic content.

An additional object is to provide sequence-starting .ballast .apparatuszwhich reduces abnormal primary windj ing temperature rise and enables greater versatility in the design of a high-reactance transformer for such apparatus.

A further specific object is to provide an improved elongated and shallow high-reactance transformer for such sequence-starting ballast apparatus.

In general, in accord with the invention, the ballasting secondary winding of a sequence-starting high-reactance transformer is divided into two secondary winding sections located on opposite sides of the primary winding with one of these ballasting secondary winding sections between the primary winding and starting sec ondary winding and in loose inductive-coupling relation with this starting winding. I have discovered that this arrangement of windings results in an unexpected improvement in the equality and wave shape of current supplied to the two discharge devices and, in addition, reduces primary winding temperature rise under abnor mal operating conditions and is more versatile enabling a wider choice in shape and size of the transformer than is possible with the entire ballasting winding located on only one side of the primary winding or with a portion thereof wound over the primary winding as suggested, for example, in United States Patent 2,683,243- Feinberg.

The novel features believed characteristic of the in vention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof can be easily understood by referring to the following description taken in connection with the accompanying drawing in which- Figure 1 is a plan view of a high-reactance transformer embodying the invention, j

Figure 2 is a schematic circuit diagram of a ballast apparatus utilizing the transformer of Figure 1,

Figure 3 is a pair of vector diagrams illustrating the phase shift and reduction in induced voltage of a starting winding of the high-reactance transformer of Figure 1 due to the presence of a portion of the ballasting winding adjacent this starting winding, and

Figure 4 illustrates the wave shape of the circulating current flowing in a starting winding circuit utilizing the invention as compared to the wave shape of starting winding circulating current of the prior art.

Referring to the drawings, apparatus embodying one form of the invention is illustrated for ballasting a pair of discharge devices shownas fluorescent lamps 10 and 11. The ballasting apparatus comprises a high-reactance transformer 12 whose construction is shown in Figure 1, and a capacitive reactor 13. Transformer 12 includes a primary winding 14 also designated by the letter P, a ballasting secondary winding divided into a pair of secondary windings 15 and 16, also designated by the letters B and B respectively, and a high-reactance or starting secondary winding 17, also designated by the letter S. The windings are arranged on a central elongated leg 18 of a shell-type magnetic core 19 with the primary winding 14 between the two ballasting secondary windings 15 and 16 and with winding 16 between the primary winding 14 and the starting winding 17. Core 19 includes outer yoke members 20 having magnetic shunts 23 defining with core leg 13 a pair of windingreceiving windows 21 and 22. Magnetic shunts 23 extend toward central leg 18 between ballasting winding 16 and starting winding 17 and terminate in small non-magnetic gaps 24. Windings 14, 15 and 16 are thus located in one core window 21 and winding 17 in the other window 22. As is well known, a series non-magnetic gap 25 is provided in the core 18 under ballasting winding 15 for adjusting the effective reactance of the ballasting winding The connections of the ballast apparatus are shown in Figure 2. Input leads or conductors 29, 30 for primary winding 14 extend toinput terminals 31 for connection to an alternating current source of relatively low frequency and voltage, for example, a 60-cycle, ll8-volt source. Ballasting windings 15 and 16 are serially interconnected by conductor 34 and in series with capacitor 13by conductor 35 across output terminals 32 and 33. Lamps 10 and 11 are connected for operation between these output terminals 32 and 33 and input leads 29 and 30 respectively such that lamps 10 and 11 are connected in series circuit relation across primary winding 14.

Starting winding 17 is connected to supply ignition voltage through capactive reactor 13 across lamp 10. In the embodiment illustrated in Figure 2, winding 17 is connected by conductors 36 and 37 to conductors 29 and 35 respectively such that it is connected from the same side of primary winding 16 as lamp 10 to the juncture of capacitive reactor 13 and ballasting winding 16. All: of the windings 14, 15, 16 and 17 are thus serially connected with lamp 11 but lamp 10 does not directly receive as part of its ignition voltage the voltage appearing across primary winding 14. Alternatively, conductor 36v may be connected to input lead 30 instead of lead 29 such that lamp 10 receives an ignition voltage equal to the sum of the generated voltage of starting winding 17 and the voltage appearing across primary winding 14. However, windings 14 and 17 are preferably polarized and connected, as indicated, in voltage opposition relative to lamp 11. Ballasting windings 15 and 16, on the contrary, are polarized and connected in voltage aiding relation to one another and preferably to primary winding 14 when connected in autotranstormer series circuit with lamps 10 and 11.

In. the operation of the ballast apparatus of the invention, an alternating current supplied to primary Winding 14 through input terminals 31 induces voltages in 'ballasting windings 15 and 16 and in starting winding 17. Although the combination of primary winding 14 and ballasting windings 15 and 16 does not generate suflicient voltage to ignite one or both lamps 10and 11, starting winding .17 has a turns ratio which does generate sufiicient voltage to ignite lamp 10. This open-circuit voltage of starting winding 17 is immediately impressed across lamp 10, through capacitive reactor 13, and lamp 10 fires. The resultant flow of current through capacitive reactor 13 and winding 17 causes a shift in phase of the voltage developed across winding 17 such that the total voltage generated by primary winding 14, starting winding 17 and ballasting windings 15 and 16 connected in series across lamp 11 is now sufiicient to ignite this lamp 11. Once lamp 11 also fires, a leading-current series circuit is established from input conductors 29, 30 through lamps 10, and 11, ballasting windings 15 and 16, and capacitive reactor 13. Starting winding 17, however, is still connected in series with lamp 11 and in parallel with lamp 10 and, despite its high reactance, would ordinarily cause an appreciable inequality or unbalance in the current drawn by each lamp.

I have discovered, however, that the location of the ballasting winding 16 between the primary winding 14 and the starting winding 17 enables a reductionin this lamp current inequality to a negligible difference. This is believed to be due to an increase in, and shift in phase of, the total fiux in the region of the core surrounding winding 16 as a result of the leakage reactance of winding 16 and the leading load current flowing through it. As a consequence, the magnetic flux which excites the adjacent starting winding 17 is shifted out-of-phase with respect to the flux generated by the primary winding 14, and the current circulating through the starting winding 17 is likewise displaced from what it would be if excited by the primary winding flux alone. This phase shift is in a direction which causes the instantaneous value of the circulatingv current in. startingwinding 17 to approach asrsnat zero when the current through lamp 11 is maximum. Since the current in lamp 10 is the summation of this circulating starting windingfcurrent and the current flowing through lamp 11, the maximum value of the current flowing in lamp is only a negligible degree greater than the maximum value of the current in lamp 11.

This shifting in phase as well as the reduction in induced voltage in starting winding 17 when lamps 10 and 11 are operating is illustrated in the vector diagrams of Figure 3 and the wave shapes of Figure 4. Figure 3a is a vector diagram of a conventional sequence-starting ballast circuit such as described, for example, in United States Patent 2,683,324-Feinberg, and Figure 3b is a vector diagram of the treminal voltages in the circuit shown in Figure 2. In these vector diagrams, the solid line vectors represent the terminal voltages with the lamps operating and all circuit connections made, and the dashed line vectors represent the terminal voltages in the same circuit with conductor 37 disconnected from conductor 35 but with lamps 10 and 11 still operating. A comparison of these vector diagrams reveals that there is a marked shift in phase and difference in amplitude in the voltage across disconnected starting winding 17 when ballasting winding 16 is located adjacent the starting winding 17 in accord with the invention. The reduction in difference voltage between conductors 37 and 35 is reflected in reduced starting winding circulating current. Tests taken on two ballasts identical except for the location of ballasting winding portion 16 showed a voltage of 365 volts between the open end of disconnected starting winding 17 and conductor 35, and a connected circulating current of 0.063 ampere when ballasting winding portion 16 was located between the primary windings 14 and 17, in accord with the invention; and a difference voltage of 473 volts between the open end of disconnected starting winding 17 and conductor 35 and a connected circulating current of 0.077 ampere when ballasting winding portion 16 was wound over the primary winding 14 in a conventional manner. The wave shapes of these circulating currents are illustrated in Figure 4, where oscillogram X is the circulating current wave in the ballast of the invention and oscillogram Y is the circulating current wave of a conventional ballast.

Another advantage of the location of the ballasting winding 16 on an opposite side of primary winding 14 from the ballasting winding 15 is the greater versatility in the design of transformer 12, since the total reactance of both ballasting windings 15 and 16 can, because of this arrangement, be adjusted to an optimum value despite the large number of turns required in order to obtain the open-circuit voltage desired to ignite lamp 11. By proper proportioning of the number of turns in each winding it is possible to obtain a wide range of desired voltage-to-reactance ratios for the combination of both windings 15 and 16. In particular, this permits an unusually shallow high-reactance transformer to be designed for operation with lamps requiring high-starting voltage; since the ballasting windings 15 and 16 may be extend ed along the axis of the device without unduly increasing the total reactance thereof and without the inequalities in current supplied to the two lamps 10 and 11 resulting from such expedients as winding a portion of the ballasting winding 15 over theprimary winding 14 in order to obtain additionalvoltage without additional reactance.

A further advantage derived from the location of ballasting winding 16 on the. opposite side of primary winding 14 from ballasting winding 15 lies in the improvement in lamp current wave form. This improvement is manifested in reduced crest factor of the lamp current wave and in reduced percent of'third harmonic current content therein. Test measurements onidentical ballasts where about one-third of the ballasting winding was relocated in accord with. the invention indicatethat theicurrent =wave crest factor for lamp 11 was improved from 1:67 'to 1.61 and that the third harmonic content in the lamp current wave decreased from 16.1% to 12.5%.

A still further advantage derived from this intermediate location of ballasting winding lies in the reduction in temperature rise of primary winding 14 if the lamp 11 position is open-circuited. Under these abnormal conditions, lamp 10 can still operate under current derived from starting winding 17. In conventional sequence-starting ballasts where the primary winding 14 is adjacent the starting winding 17, the primary winding temperature rise under such abnormal conditions was found to be in the neighborhood of 75 centigrade while substantially identical ballasts having the interposed ballast winding por tion 16 in accord with the invention had a primary winding abnormal temperature rise of only about 60 centigrade. This is believed to be due to the fact that ballast winding 16 does not carry current and thus produces no heat under such abnormal conditions, and the fact that primary winding 14- is further removed from currentcarrying starting winding 17.

Another incidental advantage of this division of ballasting winding into two windings located on opposite sides of the primary is that these three windings can now all be located in one core window 21 usually with no magnetic shunts between them.

As a specific example, a ballast constructed in accord with the invention for igniting two F96T12IS type lamps had the following outer casing dimensions-width 3%", height 1% and length 14%;". The high reactance transformer within the casing was 8 long, 2 wide, and only 1%" high. The outer yoke members of magnetic core 19 were formed by laminations .025 thick having half the width of the center leg stacked to a height of and magnetic shunts 23 located 2 from one end of the yoke laminations 20, were A wide, with an air gap of .060". The center leg core 18 consisted of a stack of .025" laminations 1 7 wide. An air gap of /1" X .090" was placed in the core 18 under the coil 15. The primary winding had 524 turns of number 22 copper wire, the starting winding had 3500 turns of number 33 copper wire and the ballasting windings 15 and 16 had a total of 2512 turns of number 28 copper wire with 1931 turns in winding 15 and 581 turns in winding 16. Capacitive reactor 13 had a capacitance of 1.7 microfarads. Operating voltages across the various secondary windings were 436 volts for winding 15, 123 volts for winding 16 and 649 volts for winding 17 Lamp current was 0.433 ampere for lamp and 0.425 ampere for lamp 11, with an input power factor of 95%.

Although I have described above specific embodiments of the invention many modifications may be made. For example, in those applications where greater leakage reactance is desired in the ballasting winding 15, shunting members may be extended between primary winding 14 and ballasting winding 15. Moreover, although for simplicity I have described the invention as applied to instant-start type lamps 10 and 11, it will be appreciated that the invention is equally applicable to heated-cathode lamps and that additional filament heating windings may be provided on high-reactance transformer 12, if desired. It is to be understood, therefore, that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1 Apparatus for sequentially igniting and operating a pair of gaseous discharge devices from an alternating current source, comprising a high-reactance transformer including a primary winding for connection to an alternating current source, a starting secondary winding, and a pair of serially interconnected ballasting secondary windings, means for connecting said ballasting windings in series circuit with said lamps across said primary windings, and a capacitive reactor in said series circuit, said starting secondary winding being connected to apply start- 6 ing voltage across said capacitive reactor and. one of said lamps in series, one of said ballasting windings being located on one side of said primary winding and the other of said ballasting windings being located on the other side of said primary winding in loose inductive-coupling relation with said starting winding.

2. Apparatus for sequentially igniting and operating a pair of gaseous discharge devices from an alternating current source, comprising a high-reactance transformer having a primary winding for connection to an alternating current source, a starting secondary winding and a pair of serially interconnected ballasting secondary windings, circuit means including a capacitive reactor for connecting said ballasting windings in series with a pair of discharge devices across said primary winding, said starting winding being connected to apply igniting voltage across said capacitive reactor and one of said discharge devices in opposition to voltage from said ballasting windings, said ballasting windings being located on opposite sides of said primary winding with one of said ballasting windings adjacent said starting winding and in loose inductive coupling relation therewith.

3. Apparatus for starting and operating a pair of fluorescent lamps from an alternating current source comprising a transformer including a primary winding for connection to an alternating current source, a starting secondary winding and a pair of ballasting secondary windings, a capacitive reactor, said ballasting windings and capacitive reactor being serially interconnected for connection in series with said lamps across said primary winding, said starting winding being connected across said capacitive reactor and one of said lamps in series for applying starting voltage across said capacitive reactor and said lamp in series, said secondary windings all exhibiting inductive reactance and said starting winding having greater reactance than said ballasting windings, one of said ballasting windings being located between said primary winding and said starting winding in inductive coupling relation with said starting winding to reduce starting winding current during operation of said lamps.

4. The apparatus of claim 3 wherein said transformer has a magnetic core with an elongated leg and said primary and secondary windings are located alongside one another on said leg with said ballasting windings on opposite sides of said primary winding.

5. The apparatus of claim 3 wherein said starting winding is wound and connected in voltage bucking relation to said primary winding and said ballasting windings are wound and connected in voltage aiding relation with said primary winding.

6. Apparatus for sequentially igniting and operating a pair of fluorescent lamps comprising a high-reactance transformer having a magnetic core with an elongated leg and an outer yoke member, a starting secondary winding, a first ballasting secondary winding, 9. primary winding, and a second ballasting secondary winding located on said leg alongside one another in the order named, a magnetic shunt from said yoke member to said leg between said starting winding and said first ballasting winding, and a capacitive reactor connected in series with said first and second ballasting windings, said starting winding being connected from one side of said primary winding to the juncture between said capacitive reactor and said ballasting winding.

7. The apparatus of claim 6 wherein said starting winding is wound and connected in voltage bucking relation to said primary winding, and said ballasting windings are wound and connected in voltage aiding relation with said primary winding.

8. The apparatus of claim 7 wherein said second ballasting winding has about three times the number of turns of said first ballasting winding.

9. The apparatus of claim 7 wherein the magnetic core has a non-magnetic gap in the series magnetic circuit of said second ballasting winding.

'10. Apparatus for igniting and operating a pair of gaseous discharge devices, comprising a high-reactance autotransformer having a primary winding, a starting secondary winding, a first ballasting secondary winding and a second ballasting secondary winding, said bal1ast ing windings being serially interconnected and said starting winding being connected from one side of the primary winding to one side of said interconnected ballasting windings, said starting winding being arranged in bucking voltage relation to said primary Winding and said ballasting windings being arranged in additive voltage relation. to said primary winding, conductors including a capacitive reactor for connecting one of said devices across References Cited in the file of this patent UNKTED STATES PATENTS 2,648,802 Kazebee Aug. 11, 1953; 2,709,231 Feinberg May 24, 1955 

